Substitute Papiss Cisse claimed a brace as leaders Chelsea's hopes of completing the Premier League season unbeaten were dashed by a 2-1 defeat at Newcastle United on Saturday.
Cisse scored twice in the second half and despite Steven Taylor being sent off for Newcastle and Didier Drogba replying late on for the visitors, Alan Pardew's side held on for a third consecutive home win over Chelsea.
Newcastle's victory means Manchester City can cut Chelsea's lead to just three points if they beat Everton later on Saturday. But Arsenal failed to capitalise, falling to a 3-2 defeat at Stoke City.
"My team lost the way I like to lose, which is to give everything and being unlucky. Only one team played to win," Chelsea manager Jose Mourinho told the BBC.
"I'm not obsessed with records and statistics. That's not for me. I want to win the league."
Chelsea recalled top scorer Diego Costa after he missed Wednesday's 3-0 win over Tottenham Hotspur through suspension and they started brightly at St James' Park, with Willian twice shooting narrowly wide.
But Newcastle defended stoutly and began to threaten, with Ayoze Perez slipping a clever pass through to Jack Colback in the 32nd minute, only for Thibaut Courtois to rush out and save.
John Mikel Obi spurned a good chance to put Chelsea ahead in the 57th minute when he headed wide from a Cesc Fabregas free-kick and within seconds, Newcastle took the lead.
Moussa Sissoko fed Sammy Ameobi on the left flank and with Gary Cahill failing to cut out the 22-year-old's low cross, Senegal striker Cisse pounced to tap home from inside the six-yard box.
Mourinho sent on Andre Schuerrle, Drogba and Filipe Luis and with 12 minutes remaining, Eden Hazard saw a shot come back off the base of the right-hand post.
Once again, Newcastle were quick to exploit their good fortune.
Colback's pass freed Sissoko and although the France midfielder was unable to get a shot away, he managed to toe the ball square to the waiting Cisse, who swept home his second goal from 12 yards.
Home captain Taylor saw red moments later after being shown a second card for upending Schuerrle and Drogba halved the deficit from the ensuing free-kick by heading in Fabregas's cross.
- Liverpool frustrated -
But despite having to endure six nail-biting minutes of injury time, Newcastle survived to deny Chelsea a club-record 24th game without defeat.
"That was about character and discipline against probably the best team in Europe at the moment," said Pardew.
"We're delighted to have given a little gee-up to the Premier League. I'm sure Jose won't agree."
As well as defending champions City, Chelsea's loss will also offer hope to third-place Southampton and fourth-place Manchester United, who meet at St Mary's on Monday.
But Arsenal squandered an opportunity to take advantage after falling to a 3-2 defeat at Stoke that left Arsene Wenger's side 13 points off the pace in sixth place.
Arsenal have struggled on their recent trips to the Britannia Stadium and on this occasion they fell behind after only 19 seconds, with Peter Crouch bundling home.
Bojan Krkic volleyed in a cross from Jonathan Walters in the 35th minute and Walters added a third on the stroke of half-time by lashing home from close range.
A Santi Cazorla penalty and an Aaron Ramsey volley took Arsenal to the verge of a comeback, but the visitors' momentum disappeared after defender Calum Chambers was shown a second yellow card for pulling back Bojan.
Liverpool saw a three-game winning run come to an end with a disappointing 0-0 draw at home to Sunderland, while Tottenham Hotspur were held to a goalless draw by Crystal Palace at White Hart Lane.
Queens Park Rangers climbed out of the relegation zone by winning 2-0 at home to Burnley on what proved an eventful afternoon for QPR striker Charlie Austin against his former club.
Austin teed up Leroy Fer's 51st-minute opener before slotting in his seventh goal of the campaign with 19 minutes left, only to then be sent off after receiving a second yellow card for a foul on Michael Keane.
QPR moved out of the bottom three at the expense of Hull City, who drew 0-0 at home to fellow strugglers West Bromwich Albion.
Source: AFP